U.S. patent number 6,046,919 [Application Number 09/275,481] was granted by the patent office on 2000-04-04 for solar power generating device.
This patent grant is currently assigned to Sanyo Electric Co., Ltd.. Invention is credited to Masaki Madenokouji, Isao Morita, Keigo Onizuka, Hisashi Tokizaki.
United States Patent |
6,046,919 |
Madenokouji , et
al. |
April 4, 2000 |
Solar power generating device
Abstract
In order to obtain a solar power generating device capable of
effectively using power generated by a solar cell, the virtual
optimum operating voltage, the MPPT minimum voltage, the MPPT
maximum voltage, and the low and high voltage change width
switching voltages used when MPPT control is carried out are
calculated on the basis of the output voltage of a solar panel
immediately before the startup of the inverter circuit in the solar
power generating device and the MPPT control is carried out on the
basis of each of the calculated voltage values.
Inventors: |
Madenokouji; Masaki
(Saitama-ken, JP), Onizuka; Keigo (Gunma-ken,
JP), Morita; Isao (Gunma-ken, JP),
Tokizaki; Hisashi (Gunma-ken, JP) |
Assignee: |
Sanyo Electric Co., Ltd.
(Osaka-fu, JP)
|
Family
ID: |
27304309 |
Appl.
No.: |
09/275,481 |
Filed: |
March 24, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Mar 30, 1998 [JP] |
|
|
10-083709 |
Mar 30, 1998 [JP] |
|
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10-083710 |
Mar 30, 1998 [JP] |
|
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10-083711 |
|
Current U.S.
Class: |
363/98; 323/906;
363/132 |
Current CPC
Class: |
G05F
1/67 (20130101); Y10S 323/906 (20130101) |
Current International
Class: |
G05F
1/66 (20060101); G05F 1/67 (20060101); H02M
007/521 () |
Field of
Search: |
;363/95,97,98,131,132
;323/906 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Berhane; Adolf Deneke
Attorney, Agent or Firm: Knobbe, Martens, Olson, Bear,
LLP
Claims
What is claimed is:
1. A solar power generating device comprising:
a solar cell, said solar cell having an output voltage;
a power converter for converting DC power output of said solar cell
into AC power;
a voltage regulator for setting a virtual optimum operating voltage
and a control voltage range of said solar cell on the basis of an
output voltage of said solar cell immediately before startup of the
power converter; and
a voltage controller for changing the output voltage of said solar
cell in stages by a predetermined voltage change width in the
direction in which the DC power output of said solar cell increases
in the control voltage range, after the power converter has started
up with the virtual optimum operation voltage taken as a target
output voltage of said solar cell.
2. A solar power generating device according to claim 1, wherein
said voltage regulator sets a switching range, which is a narrower
range than the control voltage range and which includes the virtual
optimum operating voltage, on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller makes the predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
3. A solar power generating device according to claim 1, wherein
said voltage regulator sets a fixed voltage which is a value inside
the control voltage range on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller sets the output voltage of said solar
cell as the fixed voltage when the DC power output of said solar
cell is less than a predetermined power amount.
4. A solar power generating device according to claim 2, wherein
said voltage regulator sets a fixed voltage which is a value inside
the control voltage range on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller sets the output voltage of said solar
cell as the fixed voltage when the DC power output of said solar
cell is less than a predetermined power amount.
5. A solar power generating device according to claim 1,
wherein
said voltage regulator further sets a fixed voltage on the basis of
the output voltage of said solar cell immediately before the
startup of said power converter;
said voltage controller has a first mode in which the output
voltage of said solar cell is changed in stages by a predetermined
voltage change width in the direction in which the DC power output
of said solar cell increases in the control voltage range after the
virtual optimum operating voltage has been set as a target output
voltage of said solar cell and said power converter has been
started up, and a second mode in which the output voltage of said
solar cell is set as the fixed voltage when the DC power output of
said solar cell is smaller than a predetermined power amount;
and
said solar power generating device further comprising a voltage
adjuster which increases at least one of the virtual optimum
operating voltage and the control voltage range of said solar cell
by a predetermined amount when the output power of said solar cell
is unstable.
6. A solar power generating device according to claim 5, wherein
said voltage regulator sets a determining reference voltage less
than a lower limit of the control voltage range on the basis of the
output voltage of said solar cell immediately before the startup of
said power converter, and said voltage adjuster determines that the
output power of said solar cell is unstable when the output voltage
of said solar cell is less than the determining reference
voltage.
7. A solar power generating device according to claim 5, wherein
said voltage regulator sets a switching range, which is a narrower
range than the control voltage range and which includes the virtual
optimum operating voltage, on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller makes the predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
8. A solar power generating device according to claim 6, wherein
said voltage regulator sets a switching range, which is a narrower
range than the control voltage range and which includes the virtual
optimum operating voltage, on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller makes the predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
9. A solar power generating device according to claim 1,
wherein
said voltage regulator further sets a fixed voltage on the basis of
the output voltage of said solar cell immediately before the
startup of said power converter;
said voltage controller has a first mode in which the output
voltage of said solar cell is changed in stages by a predetermined
voltage change width in the direction in which the DC power output
of said solar cell increases in the control voltage range after the
virtual optimum operating voltage has been set as a target output
voltage of said solar cell and said power converter has been
started up, and a second mode in which the output voltage of said
solar cell is set as the fixed voltage when the DC power output of
said solar cell is smaller than a predetermined power amount;
and
said solar power generating device further comprising a voltage
adjuster which resets at least one of the virtual optimum operating
voltage and the control voltage range of said solar cell on the
basis of the output voltage of said solar cell after an operation
of said power converter has stopped in accordance with the output
power of said solar cell.
10. A solar power generating device according to claim 9, wherein
said voltage regulator sets a determining reference voltage less
than a lower limit of the control voltage range on the basis of the
output voltage of said solar cell immediately before the startup of
said power converter, and said voltage adjuster determines that the
output power of said solar cell is unstable when the output voltage
of said solar cell is less than the determining reference voltage
and resets at least one of the virtual optimum operating voltage
and the control voltage range.
11. A solar power generating device according to claim 9, wherein
said voltage regulator sets a switching range, which is a narrower
range than the control voltage range and which includes the virtual
optimum operating voltage, on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller makes the predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
12. A solar power generating device according to claim 10, wherein
said voltage regulator sets a switching range, which is a narrower
range than the control voltage range and which includes the virtual
optimum operating voltage, on the basis of the output voltage of
said solar cell immediately before startup of said power converter,
and said voltage controller makes the predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
13. A method of generating solar power with a device which tracks
the maximum operating point of a solar cell comprising:
generating DC power with the solar cell, said DC power having an
output voltage;
converting said DC power into AC power with a power converter;
setting a virtual optimum operating voltage and a control voltage
range of said solar cell with a voltage regulator on the basis of
an output voltage of said solar cell immediately before startup of
the power converter; and
changing the output voltage of said solar cell with a voltage
controller in stages by a predetermined voltage change width in the
direction in which the DC power output of said solar cell increases
in the control voltage range, after the power converter has started
up with the virtual optimum operation voltage taken as a target
output voltage of said solar cell.
14. A method for generating solar power with a device which tracks
the maximum operating point of solar cell, comprising:
generating DC power with the solar cell, said DC power having an
output voltage;
converting a DC power output of said solar cell into AC power with
a power converter;
setting a virtual optimum operating voltage, a control voltage
range, and a fixed voltage with a voltage regulator on the basis of
an output voltage of said solar cell immediately before the startup
of said power converter; and
controlling the output voltage in a first mode and a second mode,
wherein in the first mode the output voltage of said solar cell is
changed in stages by a predetermined voltage change width in the
direction in which the DC power output of said solar cell increases
in the control voltage range after the virtual optimum operating
voltage has been set as a target output voltage of said solar cell
and said power converter has been started up, and wherein the
output voltage of said solar cell in the second mode is set as the
fixed voltage when the DC power output of said solar cell is
smaller than a predetermined power amount.
15. The method according to claim 14, further comprising increasing
at least one of the virtual optimum operating voltage and the
control voltage range of said solar cell by a predetermined amount
when the output power of said solar cell is unstable.
16. The method according to claim 15, further comprising setting a
determining reference voltage less than a lower limit of the
control voltage range and determining that the output power of said
solar cell is unstable when the output voltage of said solar cell
is less than the determining reference voltage.
17. The method according to claim 15, further comprising setting a
switching range, wherein the switching range is a narrower range
than the control voltage range and includes the virtual optimum
operating voltage, and making said predetermined voltage change
width smaller when the output voltage is a value falling inside the
switching range than when the output voltage is a value falling
outside the switching range when the output voltage of said solar
cell is changed in stages.
18. The method according to claim 14, further comprising resetting
at least one of the virtual optimum operating voltage and the
control voltage range of said solar cell on the basis of the output
voltage of said solar cell after an operation of said power
converter has stopped in accordance with the output power of said
solar cell.
19. The method according to claim 18, further comprising setting a
determining reference voltage less than a lower limit of the
control voltage range, wherein the output power of said solar cell
is determined to be unstable when the output voltage of said solar
cell is less than the determining reference voltage and wherein at
least one of the virtual optimum operating voltage and the control
voltage range are reset.
20. The method according to claim 18, further comprising setting a
switching range, which is a narrower range than the control voltage
range and which includes the virtual optimum operating voltage, on
the basis of the output voltage of said solar cell immediately
before startup of said power converter, and said control means
makes the predetermined voltage change width smaller when the
output voltage is a value falling inside the switching range than
when the output voltage is a value falling outside the switching
range when the output voltage of said solar cell is changed in
stages.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solar power generating device
and, in particular, to a solar power generating device for tracking
the operating point of a solar cell at the maximum point
thereof.
2. Description of the Related Art
The output voltage-output current characteristic of the solar cell
used in the solar power generating device are expressed by the
curved line shown in FIG. 4A. Accordingly, the output
voltage-output power characteristic of the solar cell are expressed
by the curved line shown in FIG. 4 B. Namely, while the output
voltage of the solar cell is between 0 (V) and a predetermined
voltage, the output power steadily increases. However, once the
output voltage of the solar cell exceeds the predetermined voltage
the output power steadily decreases. The output power at the
above-described predetermined voltage is taken as the maximum power
of the solar cell, and the operating point of the solar cell at the
above-described predetermined voltage is called the maximum power
point P.sub.M of the solar cell.
As a control for producing the maximum power from a solar cell
having this type of characteristic, a maximum power point tracking
control (hereinafter, referred to as MPPT control) is known in
which the operating point of the solar cell constantly tracks the
maximum power point P.sub.M.
This MPPT control causes a designated voltage value which becomes
the solar cell operating voltage target value to change slightly at
predetermined intervals and compares the output power from the
solar cell measured at this time with the value measured at the
previous time. By changing the above-described designated voltage
value in the direction in which the output power is constantly
increasing, the MPPT control can bring the solar cell operating
point close to the maximum output point (the optimum operating
point).
Conventionally, this type of MPPT control was carried out so that,
in order for the solar cell operating point to reach the maximum
power point in a short time when the solar cell was started, each
of the virtual optimum operating voltage, the MPPT minimum voltage
V.sub.L, and the MPPT maximum voltage V.sub.H (depending on the
type of solar cell being used) were set as fixed values and the
output power from the solar cell in the range only between the MPPT
minimum voltage V.sub.L and the MPPT maximum voltage V.sub.H was
set as the maximum.
However, the solar cell output voltage-output power characteristic
is determined not only by the type of solar cell, but also varies
according to the amount of solar radiation and changes in the
temperature around the periphery of the cell which accompany
seasonal and other variations. Namely, as is shown in FIG. 5, the
output voltage-output power characteristic changes in the direction
in which the optimum operating voltage decreases as the solar cell
peripheral temperature increases. Moreover, the output
voltage-output power characteristic changes in the direction in
which the optimum operating voltage increases when the amount of
solar radiation increases.
However, in the aforementioned conventional MPPT control, because
the virtual optimum operating voltage, the MPPT minimum voltage
V.sub.L, and the MPPT maximum voltage V.sub.H (depending on the
type of solar cell being used) were set as fixed values, there were
instances when the actual optimum operating voltage was not inside
the range between the MPPT minimum voltage V.sub.L and the MPPT
maximum voltage V.sub.H, which had been set as fixed values,
because of factors such as the temperature around the periphery of
the solar cell. This led to the problem that the power generated by
the solar cell was not able to be used effectively.
Further, the output voltage-output power characteristic differs
depending on the total surface area of the solar cell. Generally,
when a solar power generating device is installed, a plurality of
solar cell panels are connected in series so as to obtain a
predetermined output power. However, depending on conditions such
as the size of the location where the panels are installed and the
environment around that location, the number of solar cell panels
which can actually be installed sometimes differ, leading to the
output voltage-output power characteristic to also differ greatly.
Therefore, the problem exists that, conventionally, the generated
power of an actually installed solar cell can not be effectively
used because data such as the virtual optimum operating voltage are
set in advance as fixed values.
SUMMARY OF THE INVENTION
The present invention was achieved in order to solve the
above-mentioned problems and is aimed at providing a solar power
generating device which can effectively use the power generated by
a solar cell.
In order to achieve the above-described aim, the solar power
generating device according to the first aspect of the present
invention comprises: a solar cell; power conversion means for
converting a DC power output of the solar cell into a AC power;
setting means for setting a virtual optimum operating voltage and a
control voltage range of the solar cell on the basis of an output
voltage of the solar cell immediately before startup of the power
conversion means; and control means for changing the output voltage
of the solar cell in stages by a predetermined voltage change width
in the direction in which the DC power output of the solar cell
increases in the control voltage range, after the power conversion
means has started up with the virtual optimum operation voltage
taken as a target output voltage of the solar cell.
According to the solar power generating device of the first aspect
of the present invention, the DC power output of the solar cell is
converted into AC power by the power conversion means.
Moreover, the virtual optimum operating voltage and the control
voltage range of the solar cell are set by the setting means on the
basis of the output voltage of the solar cell immediately before
startup of the power conversion means. At this time, the control
voltage range is taken as including the virtual optimum operating
voltage.
In addition, after the power conversion means has been started up
with the above-described virtual optimum operating voltage taken as
the output voltage target value of the solar cell, the output
voltage of the solar cell is changed by the control means in stages
by a predetermined voltage change width in the direction in which
the DC current output of the solar cell in the above-described
control voltage range increases. Accordingly, by the operation of
this control means, the MPPT control is carried out so that the
solar cell operating point tracks the solar cell maximum power
point on the basis of the above-described virtual optimum operating
voltage and the control voltage range.
In this way, according to the solar power generating apparatus of
the first aspect of the present invention, the virtual optimum
operating voltage and the control voltage range used when the
operating point of the solar cell is controlled so as to track the
maximum power point of the solar cell are set on the basis of the
output voltage of the solar cell immediately before the startup of
the power conversion means. Therefore, the optimum virtual optimum
operating voltage and control voltage range can be obtained in
accordance with the amount of solar radiation and the temperature
around the periphery of the solar cell and other such seasonal
changes as well as the number of solar cell panels connected in
series which are actually installed. As a result, the output power
of the solar cell is able to be efficiently used.
In the solar power generating device of the second aspect of the
present invention, according to the solar power generating device
of the first aspect of the present invention, the setting means
sets a switching range, which is a narrower range than the control
voltage range and which includes the virtual optimum operating
voltage, on the basis of the output voltage of the solar cell
immediately before startup of the power conversion means, and the
control means makes the predetermined voltage change width smaller
when the output voltage is a value falling inside the switching
range than when the output voltage is a value falling outside the
switching range when the output voltage of the solar cell is
changed in stages.
According to the solar power generating device of the second aspect
of the present invention, the switching means in the solar power
generating device of the first aspect of the present invention sets
a switching range, which is narrower than the above-described
control voltage range and which includes the above-described
virtual optimum operating voltage, on the basis of the output
voltage of the solar cell immediately before the startup of the
power conversion means.
Further, when the output voltage of the solar cell is changed in
stages, the width of the voltage change (the voltage change width)
is made smaller when the output voltage is a value falling inside
the above-described switching range (the output voltage is in the
switching range) than when the output voltage is a value falling
outside the above-described switching range (the output voltage is
not in the switching range) by the control means.
In this way, according to the solar power generating device of the
second aspect of the present invention, the same effect as in the
solar power generating device of the first aspect of the present
invention can be achieved. Moreover, when the output voltage of the
solar cell is a value inside the switching range which is adjacent
to the virtual optimum operating voltage, the width of the voltage
change is made smaller than when the output voltage of the solar
cell is a value inside the switching range which is not adjacent to
the virtual optimum operating voltage. Therefore, the solar cell
operating point is able to move to the maximum power point in a
short time. In addition, because the above-described switching
range is set on the basis of the output voltage of the solar cell
immediately before the startup of the power conversion means, the
optimum switching range can be set in accordance with the amount of
solar radiation, the temperature surrounding the periphery of the
solar cell and other seasonal changes as well as with the number of
solar cell panels connected in series which are actually
installed.
In the solar power generating device of the third aspect of the
present invention, according to the solar power generating device
of the first and second aspects of the present invention, the
setting means sets a fixed voltage which is a value inside the
control voltage range on the basis of the output voltage of the
solar cell immediately before startup of the power conversion
means, and the control means sets the output voltage of the solar
cell as the fixed voltage when the DC power output of the solar
cell is less than a predetermined power amount.
According to the solar power generating device of the third aspect
of the present invention, a fixed voltage, which is a value inside
the above-described control voltage range, is set by the setting
means in the solar power generating device of the first and second
aspects of the present invention on the basis of the output voltage
of the solar cell immediately before startup of the power
conversion means.
Moreover, the output voltage of the solar cell is set as the
above-described fixed voltage when the DC power output of the solar
cell is less than a predetermined power amount.
In this way, according to the solar power generating device of the
third aspect of the present invention, the same effect as in the
solar power generating device of the first and second aspects of
the present invention can be achieved. Moreover, when the output
power is low which causes unstable operation, because the output
voltage of the solar cell is set as a fixed voltage, power can be
generated in a stable operation from the time the output power is
low until a high output power is achieved.
The solar power generating device of the fourth and fifth aspects
of the present invention comprises: a solar cell; power conversion
means for converting a DC power output of the solar cell into a AC
power; setting means for setting a virtual optimum operating
voltage, a control voltage range, and a fixed voltage on the basis
of an output voltage of the solar cell immediately before the
startup of the power conversion means; control means having a first
mode in which the output voltage of the solar cell is changed in
stages by a predetermined voltage change width in the direction in
which the DC power output of the solar cell increases in the
control voltage range after the virtual optimum operating voltage
has been set as a target output voltage of the solar cell and the
power conversion means has been started up, and a second mode in
which the output voltage of the solar cell is set as the fixed
voltage when the DC power output of the solar cell is smaller than
a predetermined power amount; and a resetting means. However, the
resetting means of the solar power generating device of the fourth
aspect of the present invention is a resetting means which
increases by a predetermined amount at least one of the virtual
optimum operating voltage and the control voltage range of the
solar cell which were set when output power of the solar cell was
unstable. The resetting means of the solar power generating device
of the fifth aspect of the present invention is a resetting means
which resets at least one of the virtual optimum operating voltage
and the control voltage range on the basis of the output power of
the solar cell after stopping the operation of the power conversion
means in accordance with the condition of the output power of the
solar cell.
According to the solar power generating device of the fourth and
fifth aspects of the present invention, the DC power output of the
solar cell is converted into AC power by the power conversion
means.
Moreover, the virtual optimum operating voltage, the control
voltage range, and the fixed voltage are set by the setting means
on the basis of the output voltage of the solar cell immediately
before startup of the power conversion means. It should be noted
that the control voltage range at this time includes the virtual
optimum operating control voltage.
In addition, at least one of a first mode, in which the output
voltage of the solar cell is changed in stages by a predetermined
voltage change width in the direction in which the DC power output
of the solar cell in the control voltage range increases, and a
second mode, in which the output voltage of a solar cell is set as
a fixed voltage when the DC power output of a solar cell is less
than a predetermined power amount, is carried out by the control
means, after the virtual optimum operating voltage has been set as
the output voltage target value of the solar cell and the power
conversion means has been started up. Accordingly, by the operation
of the first mode, MPPT control is carried out so that the solar
cell operating point tracks the maximum power point of the solar
cell by on the basis of the above-described virtual optimum
operating voltage and the control voltage range. When DC power
output of the solar cell is less than a predetermined power amount,
the second mode is executed and what is called constant voltage
control is carried out, in which the output voltage of a solar cell
is set as a fixed voltage.
In the solar power generating device of the fourth aspect of the
present invention, at least one of the virtual optimum operating
voltage and the control voltage range which were set is increased
by a predetermined amount by the resetting means when the output
power of the solar cell is unstable. Namely, as is shown in FIG. 4
A, when the output voltage of the solar cell is low then the output
power of the solar cell is unstable, and the virtual optimum
operating voltage and the control voltage range at this time are
actually located further to the left (in the direction where the
output voltage is low) of the actual maximum power point P.sub.M
(See FIG. 4 B). Consequently, by increasing by a predetermined
amount at least one of these values, the output power is made to
move in a stable direction.
In the solar power generating device of the fifth aspect of the
present invention, at least one of the virtual optimum operating
voltage and the control voltage range is reset by the resetting
means on the basis of the output voltage of the solar cell, after
the operation of the power conversion means has been stopped in
accordance with the condition of the output power of the solar
cell. Namely, when the temperature surrounding the periphery of the
solar cell changes radically due to factors such as a change in the
weather or the change between daytime and nighttime temperatures,
the output voltage-output power characteristic of the solar cell
accompanying this change changes radically and, in some cases,
stable output power cannot be obtained in the MPPT control on the
basis of the virtual optimum operating voltage and the control
voltage range which were set immediately before the startup of the
power conversion means. In these circumstances, by resetting at
least one of the virtual optimum operating voltage and the control
voltage range, on the basis of the output voltage of the solar cell
after stopping the operation of the power conversion means, this
type of problem can be solved.
In this way, according to the solar power generating device of the
fourth and fifth aspects of the present invention, the virtual
optimum operating voltage and the control voltage range used when
the operating point of the solar cell is controlled so as to track
the maximum power point of the solar cell are set on the basis of
the output voltage of the solar cell immediately before the startup
of the power conversion means. Therefore, the optimum virtual
optimum operating voltage and control voltage range can be set in
accordance with the amount of solar radiation and the temperature
around the periphery of the solar cell and other such seasonal
changes as well as the number of solar cell panels connected in
series which are actually installed. In addition, in the solar
power generating device of the fourth aspect of the present
invention, because at least one of the virtual optimum operating
voltage and the control voltage range, which were set, is increased
by a predetermined amount when the output power from the solar cell
was not stable, the output power can be stabilized and, during
periods of low output power when the operation is generally
unstable, constant voltage control is carried out to set the output
voltage of the solar cell as a fixed voltage.
In the solar power generating device of the fifth aspect of the
present invention, because at least one of the virtual optimum
operating voltage and the control voltage range is reset after the
operation of the power conversion means has been stopped in
accordance with the condition of the output power of the solar cell
on the basis of the output voltage of the solar cell, the output
power can be stabilized and, during periods of low output power
when the operation is generally unstable, constant voltage control
is carried out to set the output voltage of the solar cell as a
fixed voltage. Accordingly, in the solar power conversion device of
the fourth and fifth aspects of the present invention, power can be
generated in a stable operation from the time the output power is
low until a high output power is achieved. As a result, the output
power of the solar cell can be used efficiently.
In the solar power generating device of the sixth and seventh
aspects of the present invention, according to the solar power
generating device of the fourth and fifth aspects of the present
invention, the setting means sets a determining reference voltage
less than a lower limit of the control voltage range on the basis
of the output voltage of the solar cell immediately before the
startup of the power conversion means, and the resetting means
decides that the output power of the solar cell is unstable when
the output voltage of the solar cell is less than the determining
reference voltage. In addition, the solar power generating device
of the seventh aspect of the present invention carries out the
resetting of at least one of the above-described virtual optimum
operating voltage and the control voltage range.
According to the solar power generating device of the sixth and
seventh aspects of the present invention, a determining reference
voltage, which is less than the minimum value of the control
voltage range, is set by the setting means in the fourth and fifth
aspects of the present invention on the basis of the output voltage
of the solar cell immediately before the startup of the power
conversion means. When the output voltage of the solar cell is less
than the determining reference voltage, then the resetting means
decides that the output power of the solar cell is not stable.
Furthermore, in the solar power generating device of the seventh
aspect of the present invention, at least one of the virtual
optimum operating voltage and the control voltage range are
reset.
In this way, according to the solar power generating device of the
sixth and seventh aspects of the present invention, the same
effects are achieved as in the solar power generating device of the
fourth and fifth aspects of the present invention. In addition,
because the determining reference voltage is set on the basis of
the output voltage of the solar cell immediately before the startup
of the power conversion means, the optimum determining reference
voltage can be set in accordance with the amount of solar radiation
and the temperature around the periphery of the solar cell and
other such seasonal changes as well as the number of solar cell
panels connected in series which are actually installed. Moreover,
simply by comparing the output voltage of the solar cell with the
determining reference voltage which was set in the above-described
simple fashion, it can be decided whether or not the output power
of the solar cell is stable or not. Thus simple and precise
decision-making can be made.
In the solar power generating device of the eighth aspect of the
present invention, according to the solar power generating device
of the fourth through seventh aspects of the present invention,
setting means sets the switching range, which is narrower than the
control voltage range and which includes the virtual optimum
operating voltage, on the basis of the output voltage of the solar
cell immediately before the startup of the power conversion means,
and control means changes the output voltage of the solar cell in
stages and makes the width of the voltage change when the output
voltage is a value inside the above-described switching range
smaller than when the output voltage is a value outside the
switching range.
According to the solar power generating device of the eighth aspect
of the present invention, the setting means of the solar power
generating device of the fourth through seventh aspects of the
present invention sets the switching range, which is narrower than
the above-described control voltage range and which includes the
virtual optimum operating voltage, on the basis of the output
voltage of the solar cell immediately before the startup of the
power conversion means.
Then, every time the control means changes the output voltage of
the solar cell in stages, the control means makes the width of the
change smaller when the output voltage is a figure falling inside
the above-described switching range than when the output voltage is
a figure falling outside the above-described switching range.
In this way, according to the solar power generating device of the
eighth aspect of the present invention, the same effects can be
achieved as in the solar power generating device of the fourth
through seventh aspects of the present invention. In addition, when
the output voltage of the solar cell is a value inside the
switching range which is adjacent to the virtual optimum operating
voltage, the width of the voltage change is made smaller than when
the output voltage of the solar cell is a value inside the
switching range which is not adjacent to the virtual optimum
operating voltage. Therefore, the operating point of the solar cell
can be moved in a short time to the maximum power point. Moreover,
because the above-described switching range is set on the basis of
the output voltage of the solar cell immediately before the startup
of the power conversion means, the optimum switching range can be
set in accordance with the amount of solar radiation and the
temperature around the periphery of the solar cell and other such
seasonal changes as well as the number of solar cell panels
connected in series which are actually installed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block view showing a schematic structural view of the
solar power generating device of each embodiment of the present
invention.
FIG. 2 is a flow chart showing the operation of the solar power
generating device of the first embodiment of the present
invention.
FIG. 3 A is a flow chart showing the operation of the solar power
generating device of the second embodiment of the present
invention.
FIG. 3 B is a flow chart showing the operation of the solar power
generating device of the second embodiment of the present
invention.
FIG. 4 A is a graph showing the output voltage-output current
characteristic of a solar cell.
FIG. 4 B is a graph showing the output voltage-output power
characteristic of a solar cell used in to explain the maximum power
tracking control.
FIG. 5 is a graph showing the output voltage-output power
characteristic of a solar cell when the temperature around the
periphery of the solar cell is taken as a parameter.
FIG. 6 A is a flow chart showing the operation of a solar power
generating device of the third embodiment of the present
invention.
FIG. 6 B is a flow chart showing the operation of a solar power
generating device of the third embodiment of the present
invention.
FIG. 7 is a flow chart showing the flow of an instability detection
routine in the flow chart in FIG. 6.
FIG. 8 is a flow chart showing the flow of an instability detection
routine in another embodiment in the flow chart in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A detailed description, with reference to the drawings, will now be
given of the solar power generating device according to an
embodiment of the present invention
First Embodiment
FIG. 1 is a block view showing the overall structure when the solar
power generating device of the present invention is applied as a
system interconnection system for providing power to the load when
connected to a commercial power system. As is shown in FIG. 1, a
microcomputer 14 is provided in the solar power generating device
10 according to the present embodiment. An inverter circuit 18 is
connected to the microcomputer 14 via an IGBT driving circuit
16.
Electric power (DC power) generated by the solar panel 12
constructed of solar cells is supplied to the inverter circuit 18
via a condenser 19, a booster circuit 20, and a condenser 21. The
solar panel 12 which absorbs sunlight has several modules thereof
set in a frame, for example, and is disposed in a location such as
the roof of a building which receives solar radiation. It should be
noted here that the microcomputer 14 corresponds to the setting
means and the control means of the present invention, and the
inverter circuit 18 and the booster circuit 20 correspond to the
power conversion means of the present invention.
The inverter circuit 18 performs the function of converting the DC
power supplied from the solar panel 12 via the condenser 19, the
booster circuit 20, and the condenser 21 into AC power, based on
PMW theory, having the same frequency as commercial power (for
example, 50 or 60 hertz) on the basis of the switching signal
supplied from the IGBT driving circuit 16 controlled by the
microcomputer 14.
The power converted into AC power by the inverter circuit 18 is
supplied to a distribution board 26 via a choke transformer 22 and
a condenser 24, and is then output from the distribution board 26
into a commercial power system 48 in the shape of commercial power.
At this time, the AC power output from the inverter circuit 18 is
made to be output in the form of a sine wave by passing through the
choke transformer 22 and the condenser 24. It should be noted that
a load 46 is connected to the distribution board 26, and the load
46 operates using one of either the power supplied from the solar
power generating device 19 or the power supplied from the
commercial power system 48.
The microcomputer 14 has a generated current detection circuit 28,
a generated voltage detection circuit 30, a current detection
circuit 32, a system voltage zero cross input circuit 34, a U phase
voltage detection circuit (U phase system voltage detection
circuit) 36, and a V phase voltage detection circuit (V phase
system voltage detection circuit) 38 connected thereto.
The microcomputer 14 detects commercial power voltage and phasing
by the zero cross input circuit 34 and the U and V phase voltage
detection circuits 36 and 38 and based on the detection results
controls the IGBT driving circuit 16, and generates a switching
signal to cause the phasing and frequency of the output power from
the inverter circuit 18 to match up with the commercial power
source.
At the same time as this, the microcomputer 14 calculates the
output power and amount of change in the power (power variation) of
the solar panel 12 on the basis of the output current and output
voltage from the solar panel 12 detected respectively by the
generated current detection circuit 28 and the generated voltage
detection circuit 30. On the basis of this calculation, the
microcomputer 14 controls the MPPT control.
The microcomputer also determines whether or not the commercial
power has been cut and, if the power has been cut, opens the
connection point of the system conductor 40 provided on the
condenser 24 on the side closer to the distribution board 26 so
that the inverter circuit is cut off (paralleled off) from the
commercial power supply. At this time, the switching operation of
the inverter circuit 18 is also stopped. Namely, when the
microcomputer 14 detects that the commercial power supply has been
cut, it drives the relay coil 40A of the system conductor 40 via
the driving circuit 42.
Further, the microcomputer 14 measures the output power from the
detection results of the current detection circuit 32
An EEPROM 44 is also connected to the microcomputer 14. In the
EEPROM 44 are stored a parameter of an unillustrated system
interconnection protection device, an operating data indicating the
operating state of the solar power generating device 10, and the
like. The microcomputer 14 controls the operations of the various
pieces of equipment on the basis of the data stored in the EEPROM
44. Data is able to be electrically read from and written into the
EEPROM, and necessary data at the startup time of the solar power
generating device is read from the EEPROM 44 by the microcomputer
and where necessary data is also written to the EEPROM 44 during
the operation of the solar power generating device 10.
Next, the operation during MPPT control of the solar power
generating device 10, which is constructed as described above, will
be explained with reference to FIG. 2. It should be noted that FIG.
2 is a flow chart showing the flow of the control program executed
in the microcomputer 14 during MPPT control.
Firstly, in step 100, on the basis of the output voltage V.sub.P
from the solar panel 12 input from the generated voltage detection
circuit 30, the following calculations 1 through 5 are made. The
calculations allow: the virtual optimum operating voltage V.sub.A ;
the MPPT minimum voltage V.sub.L ; the MPPT maximum voltage V.sub.H
; the low voltage change width switching voltage V.sub.CL which is
lower than the virtual optimum operating voltage V.sub.A ; and the
high voltage change width switching voltage V.sub.CH which is
higher than the virtual optimum operating voltage V.sub.A to be
calculated. ##EQU1##
The constants in each of the above formulas (0.80, 0.70, 0.90,
0.75, 0.85) are values set in accordance with the type and so forth
of solar cell used and the present invention is not limited to
these values. The range from the above-described MPPT minimum
voltage V.sub.L to the MPPT maximum voltage V.sub.H corresponds to
the control voltage range of the present invention, while the range
from the low voltage change width switching voltage V.sub.CL to the
high voltage change width switching voltage V.sub.CH corresponds to
the switching range of the present invention.
In the next step 102, the value of the output power P.sub.S, output
the previous time from the solar panel 12, is set at zero, and in
the next step 120, the virtual optimum operating voltage V.sub.A,
calculated in the above-described step 100, is set as the target
output voltage V.sub.O of the solar panel 12. In the next step 122,
ON duty of the inverter circuit 18 (the IGBT driving circuit 16) is
controlled so that the output voltage V.sub.P of the solar panel 12
becomes the target output voltage V.sub.O.
In the next step 124, a predetermined period of time is allowed to
elapse (approximately 2-4 seconds in the present embodiment) and
then, in the next step 126, it is determined whether or not the
output voltage V.sub.P of the solar panel 12 is larger than the low
voltage change width switching voltage V.sub.CL or less than the
high voltage change width switching voltage V.sub.CH. If the
determination is affirmative, then the process moves to step 128
and 2 is substituted for the voltage change width V.sub.X and the
process then moves to step 132. On the other hand, if the
determination in step 126 is negative, the process moves to step
130 and 4 is substituted for the voltage change width and the
process then moves to step 132.
In step 132, the output power P.sub.E of the solar panel 12 is
calculated from the output voltage V.sub.P and the output current
I.sub.P of the solar panel 12. In the next step 136, the amount of
the power change .DELTA.P is calculated by subtracting the value of
the previous output power P.sub.S from the value of the output
power P.sub.E. In the next step 138, the value of the output power
P.sub.E calculated in step 132 is set as the value of the previous
output power P.sub.S.
In the next step 140, it is determined whether or not the amount of
the power change .DELTA.P is greater than 0. If it is greater than
0, the process moves to step 142 where the voltage change width
V.sub.X is added to the target output voltage V.sub.O and it is
determined whether or not the resulting value is larger than the
MPPT maximum voltage V.sub.H. If the resulting value is not larger
than the MPPT maximum voltage V.sub.H, then in step 144 the target
output voltage V.sub.O is increased by the voltage change width
V.sub.X and the process returns to step 122. On the other hand, if
it is determined in step 142 that the sum of the target output
voltage V.sub.O and the voltage change width V.sub.X is larger than
the MPPT maximum voltage V.sub.H, then the process returns to step
122 without executing step 144. Namely, in steps 140 through 144,
when the amount of the power change .DELTA.P is on an increasing
trend, the target output voltage V.sub.O is increased by the
voltage increase width V.sub.X, with the MPPT maximum voltage
V.sub.H as the upper limit, in order to increase the output power
even further.
On the other hand, if it is determined in step 140 that the amount
of the power change .DELTA.P is not greater than 0, then the
process moves to step 146 and it is determined whether or not the
amount of the power change is less than 0. If it is determined that
it is not less than 0, namely, if it is determined that the amount
of the power change is 0, then the process returns to step 122
without the target output voltage V.sub.O being changed. If it is
determined that the amount of the power change .DELTA.P is less
than 0, the process moves to step 148 and it is determined whether
or not the result when the voltage change width V.sub.X is
subtracted from the target output voltage V.sub.O is smaller or not
than the MPPT minimum voltage V.sub.L. If it is not smaller, then
in step 150, the voltage change width V.sub.X is subtracted from
the target output voltage V.sub.O and the process then returns to
step 122.
On the other hand, if it is determined in step 148 that the
resulting value when the voltage change width V.sub.X is subtracted
from the target output voltage V.sub.O is less than the MPPT
minimum voltage V.sub.L, the process returns to step 122 without
executing step 150. Namely, in steps 146 through 150, when the
amount of the power change .DELTA.P is on a decreasing trend, the
target output voltage V.sub.O is decreased by the voltage change
width V.sub.X, with the MPPT minimum voltage V.sub.L as the lower
limit, in order to increase the output power in reverse.
After this, by repeating the processes from step 122 through step
150 as described above, MPPT control can be carried out in a range
between the MPPT minimum voltage V.sub.L and the MPPT maximum
voltage V.sub.H.
In this way, in the solar power generating device according to the
first embodiment of the present invention, each time MPPT control
is carried out, the virtual optimum operating voltage V.sub.A, the
MPPT minimum voltage V.sub.L, and the MPPT maximum voltage V.sub.H
are calculated on the basis of the output voltage V.sub.P of the
solar panel 12 immediately before the startup of the inverter
circuit 18. Therefore, the MPPT control can be carried out in the
optimum range in accordance with the temperature surrounding the
periphery of the solar panel 12 and other seasonal variations, and
as a result, the output power from the solar panel 12 can be used
efficiently.
Moreover, in the solar power generating device according to the
first embodiment of the present invention, the low and high voltage
change width switching voltages V.sub.CL and V.sub.CH are used and
when the output voltage V.sub.P of the solar panel 12 is either a
value lower than V.sub.CL or a value higher than V.sub.CH, the
voltage change width is increased. When the output voltage V.sub.P
of the solar panel 12 is inside the range from V.sub.CL to V.sub.CH
which is adjacent to the virtual optimum operating voltage V.sub.A,
the width of the voltage change is made less than when the output
voltage V.sub.P of the solar panel 12 is outside the range from
V.sub.CL to V.sub.CH. Therefore, the operating point of the solar
panel 12 can be moved to the maximum power point in a short
time.
In addition, in the solar power generating device according to the
first embodiment of the present invention, the low and high voltage
change width switching voltages V.sub.CL and V.sub.CH are
calculated on the basis of the output voltage V.sub.P of the solar
panel 12 immediately before startup of the inverter circuit 18, the
optimum low and high voltage change width switching voltages
V.sub.CL and V.sub.CH can be set in accordance with the temperature
surrounding the periphery of the solar panel 12 and other seasonal
variations
Second Embodiment
The above-described first embodiment described an embodiment in
which the solar power generating device conducted only the MPPT
control. The second embodiment of the present invention conducts
constant voltage control when the output power from the solar panel
12 is low relative to the solar power generating device 10
according to the first embodiment of the present invention.
Accordingly, the microcomputer 14 in the second embodiment (refer
to FIG. 1) is provided with two control modes, namely an MPPT
control mode (tracking control mode) and a constant voltage control
mode. It should be noted that the solar power generating device of
the second embodiment of the present invention is structured in the
same way as the solar power generating device 10 of the first
embodiment of the present invention, accordingly, a description
thereof is omitted.
Next, the operation of the solar power generating device according
to the second embodiment of the present invention will be explained
with reference to FIG. 3. FIG. 3 is a flow chart showing the flow
of a control program executed by the microcomputer 14, and where
the flow chart is the same as that in FIG. 2, the same symbols are
used and an explanation thereof is omitted.
Firstly, in step 100', on the basis of the output voltage V.sub.P
of the solar panel 12 from the generated voltage detection circuit
30, the following are calculated using the above-described formulae
1 through 5 as well as formula 6 below: the virtual optimum
operating voltage V.sub.A ; the MPPT minimum voltage V.sub.L ; the
MPPT maximum voltage V.sub.H ; the low voltage change width
switching voltage V.sub.CL which has a lower voltage than the
virtual optimum operating voltage V.sub.A ; and the high voltage
change width switching voltage V.sub.CH which has a virtual optimum
operating voltage V.sub.A ; and the constant control voltage
V.sub.F. ##EQU2##
It should be noted that the constant (0.80) in the above formula 6
is a value set in accordance with the type, and the like, of solar
power generating device being used, in the same way as for the
above-described formulae, and the present invention is not limited
to this value. It should also be noted that the above-described
constant control voltage V.sub.F corresponds to the fixed voltage
of the present invention.
Thereafter, step 102 is executed, and in the next step 104, the
output power P.sub.E (=V.sub.P .times.I.sub.P) of the solar panel
12 is calculated from the output voltage V.sub.P and the output
current I.sub.P from the solar panel 12. In the next step 106, the
determination is made as to whether or not the output power P.sub.E
is less than a predetermined amount (for example, 1 kW), and if the
output power PE is less than the process moves to step 108, where
the constant voltage control mode is set. The constant voltage
control mode of step 108 corresponds to the second mode of the
present invention.
In the next step 110, the constant control voltage V.sub.F,
calculated in the above-described step 100', is set as the target
output voltage V.sub.O of the solar panel 12. Consequently, in the
next step 112, the ON duty of the inverter circuit 18 (IGBT driving
circuit 16) is controlled so that the output voltage V.sub.P of the
solar panel 12 becomes the target output voltage V.sub.O.
In the next step 114, the output power P.sub.E of the solar panel
12 is calculated from the output voltage V.sub.P and output current
I.sub.P of the solar panel 12 in the same way as in the
above-described step 104. In the next step 116, it is determined
whether or not the output power P.sub.E is less than the
above-described predetermined power amount. If the output power
P.sub.E is less than the predetermined power amount, then the
process returns to step 114. If the output power P.sub.E is not
less than the predetermined power amount, then the process moves to
step 118 mentioned below. Namely, constant voltage control is
carried out through the determining process of step 116 until the
output power of the solar panel P.sub.E is more than or equal to
the predetermined power amount.
On the other hand, if, as a result of the determination made in the
above-described step 106, it is determined that the output power
P.sub.E is not less than the predetermined power amount, the
process moves to step 118, where the tracking mode is set. This
tracking mode corresponds to the first mode of the present
invention.
After this, after the processes of steps 120 through 132 have been
carried out, in the following step 134, it is determined whether or
not the output power P.sub.E of the solar panel 12 is less than the
above-described predetermined power amount. If the output power
P.sub.E is less than the predetermined power amount, then the
process moves to step 108 and the aforementioned constant voltage
control mode is executed. If the output power P.sub.E is not less
than the predetermined power amount, then the process moves to step
136 and the processes of steps 136 through 150 are subsequently
carried out in the same way as in the above-described first
embodiment.
In this way, in the solar power generating device 10 of the second
embodiment of the present invention, the same effects as in the
above-described first embodiment can be achieved. At the same time,
because constant voltage control is obtained when the output power
is low which causes unstable operation, power can be generated in a
stable operation from the time the output power is low until a high
output power is achieved.
The explanation given in each of the above embodiments was for the
case when the voltage variable width V.sub.X during MPPT control is
taken as 2 [V] when the output voltage V.sub.P of the solar panel
12 is inside the range between the voltage change width switching
voltage V.sub.CL to the voltage change width switching voltage
V.sub.CH, and for the case when the voltage variable width V.sub.X
during MPPT control is taken as 4 [V] when the output voltage VP of
the solar panel 12 is outside the range between the voltage change
width switching voltage V.sub.CL to the voltage change width
switching voltage V.sub.CH, however, the present invention is not
limited to this and the values of these voltage change widths may
be appropriately changed in accordance with factors such as the
environment surrounding the location of the solar panel 12 and the
like.
Further, the explanation given in each of the above embodiments was
for the case when the voltages, such as the virtual optimum
operating voltage V.sub.A calculated immediately before the startup
of the inverter circuit 18, were calculated by multiplying a
constant by the output voltage V.sub.P of the inverter circuit 18,
however, the present invention is not limited to this and the
voltages may be calculated by, for example, subtracting a
predetermined value from the output voltage V.sub.P of the inverter
circuit 18.
Third Embodiment
The third embodiment of the present invention executes a control in
order to solve the problem of unstable operation in cases when the
operation of the solar power generating device 10 is unstable while
in the constant voltage control mode of the above-described second
embodiment. It should be noted that the structure of the solar
power generating device of the third embodiment is substantially
the same as the solar power generating device 10 of the first and
second embodiments (refer to FIG. 1), however, the microcomputer 14
corresponds to the setting means and the control means of the
present invention, and also to the resetting means of the present
embodiment.
Next, the operation of the solar power generating device 10
according to the third aspect of the present invention will be
described with reference to FIG. 6. It should be noted that FIG. 6
is a flow chart showing the flow of the control program executed in
the microcomputer 14.
Firstly, in step 100", on the basis of the output voltage V.sub.P
of the solar panel 12 input from the generated voltage detection
circuit 30, the above described formulae 1 through 6 and the
following formula 7 are used to calculate: the virtual optimum
operating voltage V.sub.A ; the MPPT minimum voltage V.sub.L ; the
MPPT maximum voltage V.sub.H ; the constant control voltage V.sub.F
; the instability detection voltage V.sub.E ; the low voltage
change width switching voltage V.sub.CL which has a voltage lower
than the virtual optimum operating voltage V.sub.A ; and the high
voltage change width switching voltage V.sub.CH which has a voltage
higher than the virtual optimum operating voltage V.sub.A.
##EQU3##
It should be noted that the constant (0.60) in the above formula
(7) is a value set in accordance with the type of solar cell being
used etc. and the present invention is not limited by such values.
The above-mentioned instability detection voltage V.sub.E
corresponds to the determining reference voltage of the present
invention.
After that the process moves to steps 102, 104, and 106 in the same
way as in the second embodiment of the present invention, and in
step 106, it is determined whether or not the output power P.sub.E
is less than a predetermined power amount (for example, 1 kW) and,
if the output power P.sub.E is less than the predetermined power
amount, the process moves to step 108 and the constant voltage
control mode is set.
Next, steps 110 and 112 are executed in the same way as in the
second embodiment of the present invention, and in the following
step 113, the instability detection routine shown in FIG. 7 is
executed to detect whether or not the solar power generating device
is performing unstable operations.
In step 200 of the instability detection routine, the initial
setting of the number of unstable operations HN is set to zero. In
the next step 202, a determining process is carried out to
determine whether or not unstable operations are occurring. The
determination on the unstable operations at this time is based on
whether or not the output voltage V.sub.P of the solar panel 12
input from the generated voltage detection circuit 30 is lower than
the instability detection voltage V.sub.E calculated in the
above-described step 100. Namely, as was shown in FIG. 4 A, because
the output voltage V.sub.P becomes less than the optimum operating
point, the operation of the solar cell becomes more unstable (the
output voltage V.sub.P changes easily), it is determined that
unstable operations are occurring when the output voltage V.sub.P
is less than the instability detection voltage V.sub.E.
If it is determined that unstable operations are not occurring as a
result of the determination in step 202, no process is executed and
the instability detection routine terminates.
On the other hand, if it is determined that unstable operations are
occurring as a result of the determination in step 202, the process
moves to step 204 and the number of unstable operations HN is
increased by 1. In the next step 206, an unillustrated timer built
into the microcomputer 14 is started.
In the next step 208, a first predetermined time is allowed to pass
(5 seconds in the present embodiment), and in the next step 210, it
is determined whether or not unstable operations are occurring
using the same method as in the above-described step 202. If the
determination is affirmative, the process moves to step 212 and the
number of unstable operations HN is increased by one, then the
process moves to step 214. If the determination is negative, no
processing is executed and the process moves to step 214.
In step 214, it is determined whether or not the number of unstable
operations HN is greater than a first predetermined value (5 in the
present embodiment). If the determination is negative, the process
moves to step 216 where it is determined whether or not the time
recorded by the timer which was started in step 206 has surpassed a
second predetermined time (50 seconds in the present embodiment).
If the timer has not surpassed this time, the process returns to
step 208. If the timer has surpassed this time, the instability
detection routine is terminated.
On the other hand, if as a result of the determination in step 214,
it is determined that the number of unstable operations HN is
larger than the above-described first predetermined value, the
process moves to step 218 and, after the second predetermined value
(4 in the present embodiment) has been added onto all of the
voltage values calculated in the above-described step 100", the
instability detection routine is terminated.
If it is determined as a result of the determination made in step
214 that the number of unstable operations is greater than the
above-described first predetermined value, as in the instability
detection routine in another embodiment shown in FIG. 8, the
process moves to step 219 and the inverter circuit 18 is put in a
gate block condition (with the operations of the inverter circuit
having been stopped). Then in step 220, all the voltage values
calculated in the above-described step 100" (refer to FIG. 6) are
recalculated and the instability detection routine is
terminated.
In this instability detection, when an unstable operation is
generated, during the period from that point until the
above-described second predetermined time has passed, the number of
unstable operations are counted only when the unstable operations
reoccur at intervals of the above-described first predetermined
time period. Accordingly, when the unstable operations occur singly
at time intervals which are longer than the above-described second
predetermined time, the value of the number of unstable operations
HN is not counted up to more than 2.
When an instability operation routine is terminated as described
above, in the same way as in the second embodiment of the present
invention the process moves to the next steps 114 and 116 (refer to
FIG. 6), where if the output power P.sub.E is less than the
above-described predetermined power amount, the process returns to
113. If the output power P.sub.E is not less than the
above-described predetermined power amount, the process moves to
step 118. Namely, the constant voltage control is carried out while
the instability detection routine mentioned above is repeatedly
executed through the determining process in step 116, until the
output power P.sub.E of the solar panel 12 is more than or equal to
the predetermined power amount. n the other hand, if it is
determined as a result of the determination made in the
above-described step 106 that the output power P.sub.E is not less
than the predetermined power amount, the process moves to step 118,
where the tracking control mode (MPPT control mode) is set. After
this, steps 118 through 150 (refer to FIG. 3) are executed in the
same way as in the second embodiment of the present invention.
Alternatively, as is shown in FIG. 6, the processes after step 140
may be carried out as described below.
Namely, in step 140, the determination is made as to whether or not
the amount of the power change .DELTA.P is greater than 0, and if
the determination is affirmative, the process moves to step 142
where the target output voltage V.sub.O is moved in the same
direction as the previous time by the amount of the voltage change
width V.sub.X (either increase or decrease), then the process moves
to step 160.
On the other hand, if the determination made in step 140 is
negative as to whether or not the amount of power change .DELTA.P
is greater than 0, the process moves to step 146 where it is
determined whether or not the amount of the power change .DELTA.P
is less than 0. If the determination is affirmative, the process
moves to step 148 where the target output voltage V.sub.O is moved
in the reverse direction to the previous time by the amount of the
voltage change width V.sub.X (either increase or decrease), then
the process moves to step 160. It should be noted that when the
above-described steps 142 and 148 are executed for the first time,
the target power voltage VO can be moved in either a direction of
increase or in a direction of decrease.
In step 160, it is determined whether or not the target output
voltage V.sub.O is greater than the MPPT minimum voltage V.sub.L
and less than the MPPT maximum voltage V.sub.H. If the
determination is negative, then in step 162, the target output
voltage V.sub.O is changed back to its original value (the value
before steps 142 and 148 were carried out) and the process then
returns to step 122. If the determination is affirmative, the
process returns to step 122 without carrying out the process of
step 162.
On the other hand, if it is determined in step 146 that the amount
of the power change .DELTA.P is not less than 0, namely that the
amount of the power change .DELTA.P is 0, the process moves to step
122 without changing the target output voltage V.sub.O.
Namely, in steps 140 through 162, when the amount of the power
change .DELTA.P is on an increasing trend, the target output
voltage V.sub.O is moved by the amount of the voltage change width
V.sub.X in the same direction as the previous time in order to
increase the output power P.sub.E even further, with the MPPT
minimum voltage V.sub.L set as the lower limit and the MPPT maximum
voltage V.sub.H set as the upper limit. If the amount of the power
change .DELTA.P is on a decreasing trend, the target output voltage
V.sub.O is moved by the amount of the voltage change width V.sub.X
in the reverse direction as the previous time in order to increase
the output power P.sub.E, with the MPPT minimum voltage V.sub.L set
as the lower limit and the MPPT maximum voltage V.sub.H set as the
upper limit. If the amount of the power change .DELTA.P is 0, then
the operating point is regarded as being identical to the maximum
power point and no change is made to the target output voltage
V.sub.O.
After this, by repeating the above-described steps 122 through 162,
MPPT control is carried out in the range between the MPPT minimum
voltage V.sub.L and the MPPT maximum voltage V.sub.H and when the
output power P.sub.E of the solar panel 12 is less than the
above-described predetermined power amount, the constant voltage
control mode is set.
In this way, in the solar power generating device according to the
present embodiment, the same effects as in the above-described
first and second embodiments of the present invention can be
achieved. Moreover, because during unstable operation the values of
the virtual optimum operating voltage V.sub.A, the MPPT minimum
voltage V.sub.L, and the MPPT maximum voltage and the like are
increased by the second predetermined value (4 in the present
embodiment), any unstable operations which were caused by the
values of the virtual optimum operating voltage V.sub.A, the MPPT
minimum voltage V.sub.L, and the MPPT maximum voltage V.sub.H and
the like being located to the left (the direction in which the
output voltage V.sub.O is low) of the maximum power point P.sub.M
(refer to FIG. 4B) are corrected by these values being moved in the
direction in which the operation stabilizes.
Further, if the subroutine shown in FIG. 8 is used in the
instability detection routine, because the values of the virtual
optimum operating voltage V.sub.A, the MPPT minimum voltage
V.sub.L, and the MPPT maximum voltage V.sub.H and the like are
recalculated after the operation of the inverter circuit 18 has
been stopped, unstable operations caused by factors such as sudden
changes in the temperature surrounding the periphery of the solar
panel 12 are prevented.
In the solar power generating device 10 of the present embodiment,
the low and high voltage change width switching voltages V.sub.CL
and V.sub.CH are used. If the output voltage V.sub.P of the solar
panel 12 is a lower value than the low voltage change width
switching value V.sub.CL or a higher value than the high voltage
change width switching value V.sub.CH, the voltage change widths
are increased. If the output voltage V.sub.P of the solar panel 12
falls within a range between the V.sub.CL and V.sub.CH which is
near to the virtual optimum operating voltage V.sub.A. the voltage
change width is less than the value when the output voltage V.sub.P
of the solar panel 12 does not fall within the range between
V.sub.CL and V.sub.CH. Therefore the operating point of the solar
panel 12 can be moved to the maximum power point in a short
time.
In the solar power generating device of the present embodiment, the
low and high voltage change width switching voltages V.sub.CL and
V.sub.CH are calculated on the basis of the output voltage V.sub.P
of the solar cell 12 immediately before the startup of the inverter
circuit 18, the optimum low and high voltage change width switching
voltages can be set in accordance with the temperature surrounding
the periphery of the solar panel 12 and other seasonal changes.
In addition, in the solar power generating device 10 of the present
embodiment, because constant voltage control is carried out during
low power output when the operation is unstable, power can be
generated in a stable operation from low power output times to high
output power times.
In the present embodiment, an explanation was given for when all
the voltage values calculated in step 100 were increased by the
second predetermined value when the operation was unstable,
however, the present invention is not limited to this and the
embodiment may, for example, have a constant control voltage VF
and/or an instability detection voltage VE which are not
increased.
If the instability detection routine shown in FIG. 8 is used, an
explanation was given for when all the voltage values calculated in
step 100 were recalculated when the operation was unstable,
however, the present invention is not limited to this and the
embodiment may, for example, have a constant control voltage VF
and/or an instability detection voltage VE which are not
recalculated.
In the present embodiment, an explanation was given for a
determination of whether or not the operation was unstable when in
the constant voltage control, however, the present invention is not
limited to this and the embodiment may have a determination made
when in the MPPT control.
In the present embodiment, the explanation given is for when the
output voltage V.sub.P of the solar panel 12 is in a range between
the low voltage change width switching voltage V.sub.CL and the
high voltage change width switching voltage V.sub.CH, then the
voltage change width V.sub.X in MPPT control is set as 2 (V) and
when the output voltage V.sub.P of the solar panel 12 is outside
the above range then, the voltage change width V.sub.X in MPPT
control is set as 4 (V), however, the present invention is not
limited to this and the values of these voltage change widths may
be changed appropriate to the season, location of the solar panel
12, and the like.
In the present embodiment, the explanation given was for when the
constant of the virtual optimum operating voltage VA (or other
voltages) calculated immediately before startup of the inverter
circuit 18 and the like was multiplied by the constant of the
output voltage VP from the inverter circuit 18, however the present
invention is not limited to this and the embodiment may have a
calculation made, for example, by subtracting a predetermined value
from the output voltage VP from the inverter circuit 18.
Additionally, each of the constants used in the present embodiment
(for example, the first and second predetermined times and
predetermined values in FIG. 6), may be changed where appropriate,
in accordance with the season, the location in which the solar
panel 12 has been set, and the like.
* * * * *